What game do you intend to use mods for?
Normally you will find mods, download it and just put it in your sd card using proper folder structure.
example, for witcher 3, there is a mod for 100X Gold for every quest, or a naked Ciri if you are in to that sort of thing .
these mods would normally be inside mods folder in the root of the sd card. inside the mods folder is another folder with the name of the game, i.e. Witcher 3, inside the Witcher 3 folder you create another folder with the name of the mod (i.e. 100x gold); inside this folder is another folder named contents, inside contents folder is another folder with the game's title ID (i.e. 01003D100E9C6000) and inside this folder is the rest of the rest of the file and folders which often is usually romfs, etc. etc.
so folder structure in the 100x gold mod would be like this:
mods\Witcher 3\100X gold\contents\01003D100E9C6000\romfs\content\content0\gameplay\rewards\rewards.xml